Especially photogenic are the Sultan Amir Ahmad Bathhouse(make sure you also climb up to the roof), Agha Bozorg Mosque, best visited at non-prayer times, and Khan Amir al-Dowleh Timche caravanserai in the bazaar. As the perfect stop between Tehran and Esfahan, you might want to plan your visit such that you stay the night in one of the historical homes, several of which have been converted into luxurious boutique hotels.
Kashan, Iran